1. Field of the Invention
This invention relates to mineral oils containing significant amounts of nitrogen-containing components and/or oxygen-containing components. It particularly relates to a process for substantially reducing the nitrogen and/or oxygen content of a mineral oil. This invention especially relates to a process for converting the nitrogen-containing components and/or the oxygen-containing components in a petroleum oil to sulfur-containing components.
2. Background of the Invention
Mineral oils, such as petroleum, shale oil, tar sands oil, coal derived oils, organic matter derived oils, and other natural mineral oils often contain non-metallic and metallic impurities which may adversely affect the various processes employed to refine or treat the hydrocarbon fractions of such mineral oils. The metallic impurities include compounds of nickel, vanadium, iron, calcium, magnesium, copper, lead or zinc. Especially troublesome, as catalyst poisons, are those impurities which contain nickel and vanadium. The non-metallic impurities consist of compounds containing nitrogen, sulfur and oxygen. These are often organic hydrocarbon compounds containing these impurities as heteroatoms. Both the metallic and nonmetallic impurities are undesirable in that they adversely affect such catalytic hydrocarbon processes as catalytic reforming, catalytic cracking and other catalytic processes, by poisoning the catalyst used in these processes.
Crude oils and other sources of hydrocarbons contain these impurities to varying degrees depending upon geographic origin. Crude oils containing these impurities in minor amounts usually have commanded a premium price because of their ability to be processed with catalysts for prolonged periods of time before poisoning occurs. Conversely, crude oils containing higher percentages of non-metallic and metallic impurities have been less costly because they often require additional upstream processing to remove these impurities before catalytic processing techniques could be effectively employed. In view of the higher prices commanded by the OPEC nations for premium quality crudes, lower quality crude oils have become more economically attractive provided cost effective techniques are available for the removal of the catalyst poisoning contaminants they usually contain.
Various techniques have been developed to remove significant quantities of the non-metallic and metallic contaminants from crude oils to permit efficient catalytic processing of these materials. Catalytic hydroprocessing is one of the most effective techniques for contaminant removal which has been developed heretofore and has essentially replaced such prior art techniques as acid treating, caustic treating and clay treating which were employed for contaminant removal but created severe disposal and ecological problems.
Depending upon the degree of contaminant removal desired, catalytic hydroprocessing can be adapted to operate under very mild or under very severe conditions and may be employed to treat feedstocks ranging from crude oils and reduced crudes to light virgin naphthas. Not only does hydroprocessing reduce contaminant level but it results in reduced coke production in such downstream processes as catalytic cracking which means both increased gasoline yield and higher octane of the gasoline fraction. Catalytic hydroprocessing, as its name suggests, is conducted in the presence of hydrogen, and a regenerable metal catalyst. Operating conditions usually include pressures in the range of 500 to 1500 psig and temperatures in the range of 400 to 800.degree. F. Where oxygen, nitrogen and sulfur are the principal contaminants removed, the process is referred to as hydrodesulfurization. It has been found that the oxygen and nitrogen compounds require more servere conditions for effective removal than do the corresponding sulfur compounds. Less severe hydrodesulfurization processing conditions could be employed therefore, if the nonmetallic contaminants in the crude oil or petroleum fraction consisted only of sulfur. Thus, if the oxygen and nitrogen contaminants in the mineral oil could be effectively and economically converted to the corresponding sulfur compounds, a less costly hydrodesulfurization process could be employed to complete the removal of the nometallic contaminants.
The prior art has employed hydrogen sulfide to convert nitrogen and oxygen containing organic molecules to sulfur containing molecules. For example, H.sub.2 S has been reacted with enamines at -40 to 0.degree. C. in the presence of ether to provide the corresponding dimercapto organic compounds (Magnusson, Acta Chem. Scand., 16, 1536 (1962) and 17, 273 (1963)). U.S. Pat. No. 3,306,910 of Louthan discloses that hydrogen sulfide will react with lactams at 200 to 300.degree. C. and 1 to 500 psig with a sodium hydroxide catalyst so that a sulfur atom is substituted for the carbonyl oxygen. U.S. Pat. No. 3,197,483 of Buchholz et al., relates to the replacement of the oxygen in cyclic ethers with sulfur by reaction with hydrogen sulfide in the presence of phosphotungstic acid supported on alumina. A process for converting phenols to thiophenols by reacting them with hydrogen sulfide at temperatures of 300.degree.-400.degree. C. in the presence of a vanadia catalyst is disclosed in U.S. Pat. No. 4,088,698 of Fishel et al. U.S. Pat. No. 4,143,052 of Barrault et al. relates to the preparation of a thiophene by the reaction of hydrogen sulfide with an unsaturated aldehyde, thioaldehyde, ketone or thioketone at 250.degree.-500.degree. C. in the presence of an alumina catalyst containing an alkali or alkaline earth oxide. None of this prior art suggests that the disclosed processes are applicable to a complex mixture such as a hydrocarbon petroleum fraction.
Hydroprocessing catalysts, including hydrodesulfurization catalysts, usually consist of a Group VIB and Group VIII metal in oxide or sulfide form supported on an inorganic metal oxide support having little, if any, cracking activity. Group VIB metals are usually selected from chromium, molybdenum and tungsten while the Group VIII metals are usually either cobalt or nickel. Various combinations of these two metal groups are employed. Alumina is the inorganic metal oxide which is most commonly employed as the support.
Carbonaceous materials gradually build up on a hydroprocessing catalyst slowly deactivating it. Periodically these deposits are burned off the catalyst under controlled oxidative conditions. The regenerated catalyst has a somewhat diminished activity which can be compensated for by increasing the reaction temperature slightly when the catalyst is returned to service. However, there reaches a point where the catalyst activity has been so depleted following extended use and numerous regenerations that the time between regenerations is too short to be economically attractive despite the use of increasingly higher reaction temperatures. At this point the permanently deactivated catalyst is replaced with fresh catalyst. Both permanently deactivated and temporarily deactivated catalysts have found use per se in the prior art. U.S. Pat. No. 3,378,485 of Rampino discloses that the haze in a caustic treated diesel fuel distallate can be removed by passing the distillate through a bed of deactivated but regenerable hydrodesulfurization catalyst, such as a cobalt-molybdate catalyst. U.S. Pat. Nos. 3,850,744 and 3,876,532 of Plundo et al. relate to the use of a permanently deactivated hydrotreating catalyst. Plundo et al. found that such catalysts still possess sufficient activity for use in a relatively low pressure and mild hydrotreating process for virgin middle distillates such as, straight run furnace oil, jet fuel or kerosene whose macaptan level only requires a mild hydrotreating. Neither Rampino nor Plundo et al. suggest using a deactivated hydroprocessing catalyst or a fresh catalyst containing the metals of a deactivated hydroprocessing catalyst to convert nitrogen and oxygen components in a mineral oil to the corresponding sulfur compounds.
It is an object of this invention to provide a process for reducing the oxygen and nitrogen content of a mineral oil fraction so as to reduce the severity normally required in a hydrodesulfurization process.
It is a further object of this invention to convert the nitrogen and oxygen containing components in a mineral oil to the corresponding sulfur compounds which in turn can effectively be removed in a subsequent hydrodesulfurization process operated under less severe conditions than would otherwise be required.